AQA GCSE Physics Physics Paper 1 (Foundation), June 2025: Question 4

✅ Correct Answers

• 04.1: The speed increased [1 mark]
• 04.2: The kinetic energy increased [1 mark]

💡 Key Knowledge

The temperature of a gas is directly proportional to the average kinetic energy of its particles:

• Heating → thermal energy transfers to the particles' kinetic stores.
• Higher kinetic energy ( E_k = ½mv² ) means particles move with a greater average speed.

🧠 Exam Technique

These two questions are paired: if particle speed increases, kinetic energy must also increase. Always keep these two concepts tightly linked in kinetic theory questions.

✅ Correct Answers

• 04.3: The number of collisions each second increased [1 mark]
• 04.4: The force exerted increased [1 mark]

💡 What Causes Gas Pressure?

Gas pressure is defined as the total normal force exerted by particles colliding with a unit area of the container walls:

• Faster particles hit the walls more frequently (more collisions per second).
• Each impact exerts a greater force because the change of momentum is larger.
• Both factors cause total pressure inside the rigid flask to rise.

❌ Common Errors

Students often miss the phrase "each second" and confuse total collisions with collision rate. In a fixed volume flask, faster particles travel from wall to wall quicker, raising the rate of collisions.

✅ Correct Matching

• Liquid ➔ Bottom box (particles touching, irregular/random arrangement)
• Solid ➔ Middle box (regular repeating grid/lattice, tightly packed in rows)
• Gas ➔ Top box (widely separated, random positions, few particles)

❌ Common Drawing / Matching Pitfalls

• Drawing multiple lines: The mark scheme strictly states: "do not accept more than one line from a box on the left". If you draw two lines from "Liquid", you forfeit that mark.
• Liquid misconception: Thinking liquid particles are far apart. In liquids, particles are still touching/close together, just randomly arranged!

✅ Correct Answers

• 04.6: Liquid [1 mark]
• 04.7: Solid [1 mark]

📐 Visualising the Temperature Scale

Nitrogen values given: Melting Point = -210 °C, Boiling Point = -196 °C.

• Below -210 °C ➔ Solid
• Between -210 °C and -196 °C ➔ Liquid
• Above -196 °C ➔ Gas

Since -200 °C sits between -210 °C and -196 °C, nitrogen is a liquid.

❌ The Negative Number Trap

Many students see the digits 200 and think it is lower than 210 . Remember that with negative numbers:

-210 °C < -200 °C < -196 °C

-200 °C is warmer than the melting point (-210 °C), so it has already melted!

💡 Kinetic vs Potential Energy in Internal Energy

Internal energy is the sum of kinetic energy and potential energy:

• Kinetic energy depends ONLY on temperature: The question states temperature is constant during melting, so average kinetic energy stays the same.
• Potential energy relates to particle separation: Energy transferred from heating breaks or weakens intermolecular bonds, moving particles slightly further apart, so potential energy increases.

🧠 Top Examiner Tip

Whenever a question mentions that a substance is changing state (melting or boiling) at a constant temperature, immediately think:

👉 Temperature constant = Kinetic energy stays the same.

👉 Bonds breaking = Potential energy increases.